In the prior art a number of security and object location systems are taught. In U.S. Pat. No. 5,543,797 a monitoring system is described for monitoring the location of mobile objects in a structure. This monitoring system provides an R. F. transponder for each mobile object or person. A number of transceivers are position around the monitored structure to receive transmitted signals from the transponders. Each transponder periodically transmits a unique identification code that is received by one or more of the transceivers that are closest thereto. The transceivers measure the strength of the signals received from the transponders and forward this information to a central controller. The central controller knows that a transponder is located in an area around the particular transceiver that measures and indicates the highest signal strength. The central controller can transmit commands through the particular transceivers to selected transponders, including audible messages to a person having a transponder, via an earphone. However, this monitoring system can only indicate a general area in which a specific transponder is located. It cannot provide a fairly specific position at which a specific transponder is located.
U.S. Pat. No. 3,419,865 teaches an arrangement for continuously determining and displaying the location of a number of mobile police vehicles for the purpose of indicating their exact relative locations within a metropolitan area. Each police vehicle has a transceiver that periodically transmits an identification signal within an assigned time slot in a time division multiplexing arrangement. An identification signal is received by at least three stationary receivers, each having clocks synchronized to a central master clock. The physical position of a vehicle is reflected in the time difference that the identification signal transmitted from the vehicle is received at each receiver. This information is transmitted back to a central computer that calculates the position of the vehicle on a map relative to the position of the stationary receivers. This arrangement will not work in an environment of adjacent rooms where it is desired to locate transceivers in each room, because radio waves generated by a transceiver in one room will travel through the walls and be received by receivers in adjacent rooms.
U.S. Pat. No. 5,512,879 teaches apparatus for preventing infant mix ups and kidnappings in hospitals. A miniature electronic security tag is affixed to the ankle of a newborn infant. Periodically, the tag transmits a unique encoded identity signal that is received by strategically placed radio receivers within a hospital. Attempts to remove a tag are detected and transmitted to the receivers. A central computer continuously determines the identity and location of each tagged infant in the hospital. In the event that an unauthorized person attempts to leave the hospital or a smaller monitored area with an infant, or if a tag is removed, an alarm is sounded. However, this monitoring apparatus only detects if an infant having a security tag is taken through a doorway equipped with a monitor receiver. It does not indicate the location of an infant within a larger area.
Thus, there is a need in the prior art for a security monitoring system that monitors the exact location of, and providing security for, mobile objects including children.